In accordance with Winchester fixed disk drive technology, a data transducer head slider "flies" upon an air bearing effect in very close proximity, e.g. 4-5 micro-inches, to a proximate disk data storage surface. The air bearing exists only when the storage disk is rotating. When the disk stops rotating, in a "contact-start-stop" disk drive, the head sliders "land" on the disk surface. Storage media is frequently provided with an overcoat or a lubricating coat in order to withstand direct contact between the head slider and the storage surface. Consequently, some disk drive manufacturers permit the slider to land at any location of the data storage disk.
Direct contact between the disk and the heads may abrade or interfere with the storage media. Data recorded at the location of direct contact may be changed, or a permanent defect known as a "hard error" may develop. Accordingly, many disk drive manufacturers provide a dedicated landing zone for the head sliders. This landing zone is usually selected to be at an innermost useable radius of the data storage disk, as magnetic storage cells or domains are fewest at the radially inwardmost area of the disk.
Head sliders are typically formed of highly lapped ferro ceramic material. The edges of the rails are very sharp. Radial displacement of the head sliders while in contact with the data storage surface has proven very detrimental to the integrity of the storage surface. Such movements may gouge, scratch or scrape away the magnetic data storage coating. Thus, a latch is conventionally provided to lock the head positioner assembly (herein "actuator") at the landing zone when power is removed from the disk drive and/or the spindle motor is not spinning (as may occur during a reduced power standby state).
Actuator latches have taken many forms. One approach pioneered by the assignee of the present invention has been an aerodynamically released actuator latch which operates to release the actuator in response to airflow generated by disk rotation which overcomes a bias force; see, e.g. commonly assigned U.S. Pat. Nos. 4,538,193; 4,692,829 and 4,647,997. One drawback of the approaches described in these patents is that with small disk diameters, such as 3.5" and below, unenhanced airflow from a single disk is generally insufficient to enable the aerodynamic actuator latch to operate reliably within a manufacturable design for mass production of disk drives.
Bistable electromagnetic latches have been proposed in the prior art. Pertinent examples include U.S. Pat. No. 4,881,139 to Hazebrouck; U.S. Pat. No. 4,654,735 to Izraelev et al.; U.S. Pat. No. 4,965,684 to Stefansky; and U.S. Pat. No. 4,903,157 to Malek. Other patents considered in preparation of the application leading to this patent include U.S. Pat. Nos. 4,890,176 and 4,947,274 to Casey et al.; U.S. Pat. No. 4,868,695 to Quatro et al.; U.S. Pat. No. 4,851,943 to Perry; U.S. Pat. No. 4,764,831 to Patel; U.S. Pat. No. 4,751,595 to Kishi et al.; U.S. Pat. No. 4,706,142 to Hattori et al.; U.S. Pat. No. 4,686,595 to Bryer; U.S. Pat. No. 4,660,120 to Manzke et al.; U.S. Pat. No. 4,139,874 to Shiraishi; U.S. Pat. No. 4,594,627 to Viskochil et al.; and U.S. Pat. No. 4,716,480 to Wiens et al.
Commonly assigned U.S. patent application No. 07/696,629, filed on May 7, 1991, now U.S. Pat. No. 5,208,713 and entitled, "Bistable Magnetic/Electromagnetic Latch for Disk File Actuator," describes an improved bistable latch employing magnetic and electromagnetic elements for latching a disk file actuator so that data transducer heads are parked and maintained at a predetermined landing zone. Although this device works effectively for its intended purpose, it requires a number of components and is relatively expensive to make. In addition, this prior latch operated satisfactorily within only a narrow range of operating currents, limiting the range of power supplied from an external power supply.
Another approach which is pertinent to the present invention is described in U.S. Patent No. 5,025,335 to Stefansky. This patent describes an actuator latch employing a fixed capture permanent magnet assembly for capturing a radially extended, magnetically permeable capture body of the rotary voice coil actuator as the landing zone is approached. One drawback of fixed capture magnets is their tendency to EXERT a bias force upon the actuator as the vicinity of the parking zone is reached, thereby interfering with servo loop control of head position at the radially innermost tracks.
Hence, despite the numerous and varied approaches exemplified by the above patents, hitherto unsolved need has remained to continue to develop effective, low cost mechanisms for latching a disk drive actuator to maintain the heads in the landing zone when the disk is not spinning.